1. Field of the Invention
The present invention relates to a laminated optical waveguide film, a method of producing the same, as well as an optical waveguide module using the laminated optical waveguide film.
2. Description of the Related Art
As a method of producing a polymer optical waveguide, (1) a method of impregnating films with a monomer, selectively exposing a core part to light to change a refractive index, and laminating the films (selective polymerization method), (2) a method of coating a core layer and a clad layer, and forming a clad part using reactive ion etching (RIE method), (3) a method using a photolithographic method in which exposure and developing are performed using an ultraviolet-ray curable resin in which a photosensitive material has been added to a polymer material (direct exposure method), (4) a method utilizing injection molding, and (5) a method of coating a core layer and a clad layer, and exposing a core part to light to change a refractive index of the core part (photobleaching method) have been proposed.
The selective polymerization method of (1) has a problem with respect to lamination of films.
Methods of (2) and (3) have a high cost due to use of a photolithographic method. The method of (4) has a problem with respect to precision of the resulting core diameter. In addition, the method of (5) has a problem that a sufficient difference in refractive index between a core layer and a clad layer cannot be realized.
Currently, practical methods excellent in performance include only the methods of (2) and (3), but these methods have a problem with respect to a cost as described above. Further, none of the method of (1) to (5) is suitable for forming a polymer optical waveguide on a flexible plastic substrate having a large area.
In contrast, as a method entirely different from the aforementioned conventional methods of producing a polymer optical waveguide, the present inventors invented and filed application for a method of producing a polymer optical waveguide by using a mold as shown in Japanese Patent Application Laid-Open (JP-A) No. 2004-29507, JP-A No. 2004-86144, and JP-A No. 2004-109927.
This method can mass-produce a polymer optical waveguide, extremely simply and at a low cost. In addition, although this is a simple method, it is possible to manufacture a polymer optical waveguide having little waveguide loss, and it is possible to simply manufacture a polymer optical waveguide having any pattern shape as long as a mold therefor can be manufactured. Further, it has enabled manufacture of an optical waveguide on a flexible substrate, which has previously been difficult.
Further, the present inventors previously filed an application for a method of forming a laminate-type polymer optical waveguide which was published as JP-A No. 2004-069742. If a polymer optical waveguide having a laminate structure can be realized, for example, light can be easily led to an optical fiber array of a type in which many optical fibers are laminated, and a large capacity data transmitting optical module can be easily manufactured.
As laminate-type polymer optical waveguides, those of JP-A No. 2000-39530 and JP-A No. 11-183747 are known. However, laminate-type polymer optical waveguides disclosed in these patent publications have a very complicated structure, it is necessary to embed a mirror or a lens in the polymer optical waveguide, and it is impossible to manufacture it at a low cost. In addition, also when a polymer optical waveguide and light receiving and emitting elements are laminated, it is necessary to perform positioning at a high precision, and a cost necessary for packaging has been a great problem.
Further, it is advantageous from the viewpoint of packaging density that an optical waveguide module is manufactured by combining a laminate-type polymer optical waveguide with a planer light emitting element, such as a vertical cavity surface emission laser (VCSEL), or a planer light receiving element. Moreover, when many elements are used, a transmission rate can be further improved. However, in order to combine VCSEL with a laminate-type optical waveguide, it is necessary to vertically package the VCSEL relative to a waveguide plane, or combine a 45° reflection mirror structure and a microlens as described in Japanese Patent No. 3062345. This is because distances between an optical element and a waveguide core are different depending on a number of lamination layers in the case of a laminate-type optical waveguide because of the existence of corresponding 45° mirrors , and effective coupling is impossible unless light is collimated. For this reason, it is necessary to arrange a microlens structure on a light emitting element side, resulting in higher costs. Further, in order to couple a light receiving element, a microlens structure becomes necessary at each core end surfaces, respectively. It is extremely difficult to incorporate this structure into an ordinary process for manufacturing a polymer waveguide, and moreover, this leads to higher cost. In the case of a structure other than this structure, a countermeasure for crosstalk is difficult, and this becomes a problem for realizing an optical module using such a planer packaging laminate waveguide structure.